A light emitting diode (LED) is a semiconductor device capable of converting electrical energy into visible light and radiation energy when electrical current flows between the anode and the cathode due to a voltage applied on both terminals of the semiconductor device. When the current passes through the LED in the forward direction, electrons recombine with holes and the extra energy is released in the form of light. The wavelength of the emitted light corresponds to the material and the energy associated with electron-hole pair recombination. The advantages of using the LED include a low operating voltage, low power consumption, high illuminating efficiency, very short response time, pure light color, high structural firmness, high impact resistance, excellent performance reliability, light weight, cost effectiveness, long service life, and so on. Therefore, the incandescent bulbs or mercury vapor lamps used in the conventional lighting system are gradually replaced by LEDs in many applications.
By using three primary color LEDs, for example a combination of red (R), green (G) and blue (B) LEDs, and adjusting the brightness of the LEDs, light output beams with various emission colors can be produced. Generally, the lighting system has a user operation interface (e.g. a button or a knob) or a remote controller. By triggering the user operation interface or using the remote controller, the brightness or the color of the light output from the lighting system can be controlled accordingly.
Recently, remote controllers become essential components of many kinds of household electrical appliances such as TV sets, DVD players, audio equipments, air conditioners, and so on. That is, the use of remote controllers may facilitate manipulation of these household electrical appliances. Since various kinds of electrical appliances have their own remote controllers, the user is often confused with a lot of remote controllers and the selection of the actual remote controller becomes troublesome. Moreover, too many remote controllers are neither cost-effective nor user-friendly. For reducing the dependence on remote controllers, a lighting system has been developed in WO 2006/056814, which is entitled “PROXIMITY SENSOR DIMMING CONTROL FOR A LIGHT”, and the contents of which are hereby incorporated by reference. FIG. 1 is a schematic diagram illustrating a lighting system disclosed in WO 2006/056814. As shown in FIG. 1, the lighting system 1 comprises an infrared transmitting and receiving unit 10 and a light-emitting unit 11. When an object 100 (e.g. a user's hand) is positioned in the sensing range of the infrared transmitting and receiving unit 10, an infrared beam 12 emitted by the infrared transmitting and receiving unit 10 is reflected by the object 100, and the reflected infrared beam 13 is then transmitted to an infrared receiver 101 of the infrared transmitting and receiving unit 10. Generally, the intensity of infrared light 13 reflected from the object 100 and received by the infrared transmitting and receiving unit 10 is dependent on the inverse square of the distance between the infrared transmitting and receiving unit 10 and the object 100. By determining the movement of the object 100 away from or toward the infrared transmitting and receiving unit 10, the brightness or the color of the light output from the light-emitting unit 11 of the lighting system 1 is controlled accordingly.
The approach of controlling the brightness or the color of the output light from the light-emitting unit 11 of the lighting system 1, however, still has some drawbacks. For example, since the intensity of infrared light detected by the infrared transmitting and receiving unit 10 is readily interfered with the background brightness, the detecting accuracy is deteriorated. In addition, the operating range of the infrared transmitting and receiving unit 10 is highly dependent on the intensity of the received infrared light. As known, the operating range is only up to approximately 30 centimeters.
Therefore, there is a need of providing an improved lighting system and a light output control method to obviate the drawbacks encountered from the prior art.